This invention relates to the preparation of polyurethane and/or polyurea elastomers, particularly to polyurethane and/or polyurea elastomers which are prepared from a high molecular weight prepolymer.
Polyurethane elastomers are being used in a growing variety of applications. Since the development of reaction injection molding (RIM) techniques permitted the rapid production of molded parts, polyurethane have been developed for many end uses. For example, low to moderate modulus polyurethanes have found use as static elastomers, such as automobile bumper covers, front and rear fascia for automobiles, beer keg skirts and the like. High modulus polyurethanes are being explored for use in making automobile doors, fenders, quarter panels and similar exterior parts.
In preparing polyurethane and/or polyurea elastomers, the common practice is to react a polyisocyanate, or a quasi-prepolymer thereof, with a relatively high equivalent weight active hydrogen containing material, usually a polyether polyol or aminated derivative thereof, and a low equivalent weight polyamine or polyol (chain extender). The polyol provides "soft segments" to the elastomer, i.e. provides the elastomer with elasticity, low temperature properties and impact strength. The chain extender reacts with the polyisocyanate to provide "hard segments", i.e. contributes stiffness, high temperature properties, and tensile strength.
It is generally desirable in most circumstances to form a polymer in which the soft and hard segments are well phase-segregated. In most cases, good phase segregation leads to improved properties, especially good thermal properties. Thus, it is desirable to provide a process whereby phase segregation is improved. Improved phase segregation may enable the practitioner to employ lesser amounts of chain extender in making a polymer of a given flexural modulus. Since the chain extender is often a relatively expensive component of the polymer, this represents a significant economic advantage.
In addition, it is often desirable to improve the "toughness" of polyurethane and/or polyurea polymers, that is, improve the tear properties and/or the impact strength thereof.